ISPConfig 3 - Mail Flow

Can someone describe exactly how mail flows through the standard ISPConfig 3 setup? I have investigated the configs to some extent and have a basic idea, but there seems to be some redundancy I don't quite understand.

Here is my basic understanding:

Postfix receives mail, forwards to amavisd-new, which then scans with clamav, and spamassasin, and then sends back to postfix.....

Does postfix then send to maildrop for delivery? How can one verify this?

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Is virus scan and spam filtering enabled globally by default unless turned off in a domain?
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Also, how is getmail used exactly?

If this is documented reasonably straight forward somewhere I would be happy for a pointer.